Display systems are used for example in industrial automation devices. Industrial automation devices are for example devices for regulation and/or control purposes (a programmable logic controller PLC for example), a switched mode power supply, a power converter, a contactor etc. Such devices are used in particular in control engineering and drive engineering. The industrial automation devices are subject to an ever increasing extent to demands for compactness with enhanced functional capabilities and a growing interface framework. In conjunction with basic conditions such as “side-by-side mounting” and predefined connector assemblies or cable cross-sections for example, this leads to the problem that the space available on the front face of the device becomes ever less. In a control cabinet, industrial automation devices are positioned alongside one another for example on a rail. Only a top side, an underside and a front face of the industrial automation device are then available for connection of cables to the industrial automation device. If it should be easily possible to read information from the industrial automation device, without needing to disassemble the industrial automation device for example, then the industrial automation device has a display system which is situated in particular on the front face of the industrial automation device. Since easily accessible sides of the industrial automation device, such as in particular the front face, are however mostly too small to accommodate all the displays, the displays are either reduced in size, which impairs their readability, or displays are placed at positions on the industrial automation device which are difficult to access. If the industrial automation device has an identification plate for example, then in the absence of a better and more easily accessible space this identification plate is for example mounted on one side of the industrial automation device, which is provided so that in the installed state a further industrial automation device adjoins it at this side in the control cabinet. The identification plate as a passive form of a display system can consequently only be read prior to installation or after removal. In addition to the type and/or the serial number, the identification plate also carries a bar code for example. A display system which can be operated electrically is for example provided on the front face of the industrial automation component. Such display systems which can be operated electrically are for example LED displays, LCD displays, OLED displays, etc. These display systems which can be operated electrically have a display panel and if applicable also a control electronics unit for the display panel. An input unit is for example also associated with the display system which can be operated electrically, using keys for example. The input unit can however advantageously also be combined with the display system in the form of a touch-sensitive display panel (touch-screen).
Display panels, be they display panels which can be operated electrically, whereby these constitute active display panels, or also passive display panels (an identification plate for example), can only be miniaturized up to a certain limit if they are to remain capable of being read by a person without any auxiliary means. Displays, and also operating controls, must have a certain minimum size for ergonomic reasons.
If the space for optimum mounting of the display system or display systems (a display and an identification plate for example) is limited, then it has previously been necessary to accept compromises. One compromise is for example to mount the identification plate at a position on the industrial automation device which is difficult to access or also on another device, or also to reduce the size of the display panel, with the result that the clarity of the display suffers. A further known measure is to reduce the size of input keys on an input unit which is associated with the display system.
A display device is known from US 2004/0257317 A1, in which a liquid crystal display is arranged in front of a poster. The poster can be viewed through the liquid crystal display. Text can simultaneously be displayed on the liquid crystal display.
A hand-held unit is known from US 2005/0052341 A1, which has two display panels arranged behind one another, whereby the rear display panel can be viewed through the front display panel.
FR 2 818 787 A describes a display device in which graphics can be presented on a screen. An illumination source is arranged behind the screen. With the aid of the illumination, symbols and texts can be presented, which can be viewed from the front together with the graphic situated on the screen.